3/3 Use MessageSendInstructions instead of PendingOnionMessage

Now that the `MessageRouter` can `create_blinded_paths` forcing
callers of the `OnionMessenger` to provide it with a reply path up
front is unnecessary complexity, doubly so in message handlers.

Here we take the next step towards untangling that, moving from
`PendingOnionMessage` to `MessageSendInstructions` for the outbound
message queue in `AsyncPaymentsMessageHandler`. Better, we can also
drop the `c_bindings`-specific message queue variant, unifying the
APIs.

Here we also drop `PendingOnionMessage` entirely.

By unifying the response type with the outbound message queue type,
this also fixes #3178.

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -71,7 +71,7 @@ use crate::offers::parse::Bolt12SemanticError;
 use crate::offers::refund::{Refund, RefundBuilder};
 use crate::offers::signer;
 use crate::onion_message::async_payments::{AsyncPaymentsMessage, HeldHtlcAvailable, ReleaseHeldHtlc, AsyncPaymentsMessageHandler};
-use crate::onion_message::messenger::{Destination, MessageRouter, PendingOnionMessage, Responder, MessageSendInstructions};
+use crate::onion_message::messenger::{Destination, MessageRouter, Responder, MessageSendInstructions};
 use crate::onion_message::offers::{OffersMessage, OffersMessageHandler};
 use crate::sign::{EntropySource, NodeSigner, Recipient, SignerProvider};
 use crate::sign::ecdsa::EcdsaChannelSigner;
@@ -10962,7 +10962,7 @@ where
 
 	fn release_held_htlc(&self, _message: ReleaseHeldHtlc) {}
 
-	fn release_pending_messages(&self) -> Vec<PendingOnionMessage<AsyncPaymentsMessage>> {
+	fn release_pending_messages(&self) -> Vec<(AsyncPaymentsMessage, MessageSendInstructions)> {
 		Vec::new()
 	}
 }

lightning/src/onion_message/async_payments.rs

@@ -12,7 +12,6 @@
 use crate::io;
 use crate::ln::msgs::DecodeError;
 #[cfg(not(c_bindings))]
-use crate::onion_message::messenger::PendingOnionMessage;
 use crate::onion_message::messenger::{Responder, MessageSendInstructions};
 use crate::onion_message::packet::OnionMessageContents;
 use crate::prelude::*;
@@ -40,23 +39,7 @@ pub trait AsyncPaymentsMessageHandler {
 	///
 	/// Typically, this is used for messages initiating an async payment flow rather than in response
 	/// to another message.
-	#[cfg(not(c_bindings))]
-	fn release_pending_messages(&self) -> Vec<PendingOnionMessage<AsyncPaymentsMessage>> {
-		vec![]
-	}
-
-	/// Release any [`AsyncPaymentsMessage`]s that need to be sent.
-	///
-	/// Typically, this is used for messages initiating a payment flow rather than in response to
-	/// another message.
-	#[cfg(c_bindings)]
-	fn release_pending_messages(
-		&self,
-	) -> Vec<(
-		AsyncPaymentsMessage,
-		crate::onion_message::messenger::Destination,
-		Option<crate::blinded_path::message::BlindedMessagePath>,
-	)> {
+	fn release_pending_messages(&self) -> Vec<(AsyncPaymentsMessage, MessageSendInstructions)> {
 		vec![]
 	}
 }

lightning/src/onion_message/messenger.rs

@@ -410,38 +410,6 @@ pub enum MessageSendInstructions {
 	}
 }
 
-/// An [`OnionMessage`] for [`OnionMessenger`] to send.
-///
-/// These are obtained when released from [`OnionMessenger`]'s handlers after which they are
-/// enqueued for sending.
-#[cfg(not(c_bindings))]
-pub struct PendingOnionMessage<T: OnionMessageContents> {
-	/// The message contents to send in an [`OnionMessage`].
-	pub contents: T,
-
-	/// The destination of the message.
-	pub destination: Destination,
-
-	/// A reply path to include in the [`OnionMessage`] for a response.
-	pub reply_path: Option<BlindedMessagePath>,
-}
-
-#[cfg(c_bindings)]
-/// An [`OnionMessage`] for [`OnionMessenger`] to send.
-///
-/// These are obtained when released from [`OnionMessenger`]'s handlers after which they are
-/// enqueued for sending.
-pub type PendingOnionMessage<T> = (T, Destination, Option<BlindedMessagePath>);
-
-pub(crate) fn new_pending_onion_message<T: OnionMessageContents>(
-	contents: T, destination: Destination, reply_path: Option<BlindedMessagePath>
-) -> PendingOnionMessage<T> {
-	#[cfg(not(c_bindings))]
-	return PendingOnionMessage { contents, destination, reply_path };
-	#[cfg(c_bindings)]
-	return (contents, destination, reply_path);
-}
-
 /// A trait defining behavior for routing an [`OnionMessage`].
 pub trait MessageRouter {
 	/// Returns a route for sending an [`OnionMessage`] to the given [`Destination`].